Identify the paris which are not of isotopes?

Options

A. `._(6)^(12)X, _(6)^(13)Y`
B. `._(17)^(35)X, _(17)^(37)Y`
C. `._(6)^(14)X, _(6)^(13)Y`
D. `._(4)^(8)X,_(5)^(8)Y`

Explanation

To identify the pairs that are not isotopes, we need to understand the definition of isotopes. Isotopes are atoms of the same element that have the same atomic number (number of protons) but different mass numbers (total number of protons and neutrons).

### Step-by-Step Solution:

1. **Understand the Definition of Isotopes**:
- Isotopes have the same atomic number but different mass numbers.
- Example: Carbon-12 (¹²C) and Carbon-14 (¹⁴C) are isotopes of carbon because they both have an atomic number of 6 but different mass numbers.

2. **Analyze the Given Options**:
- We have four pairs to analyze. We will check each pair to see if they meet the criteria for being isotopes.

3. **Option 1: X (12, 6) and Y (13, 6)**:
- Atomic numbers: Both are 6 (same).
- Mass numbers: 12 and 13 (different).
- Conclusion: They are isotopes.

4. **Option 2: X (35, 17) and Y (37, 17)**:
- Atomic numbers: Both are 17 (same).
- Mass numbers: 35 and 37 (different).
- Conclusion: They are isotopes.

5. **Option 3: X (14, 6) and Y (14, 7)**:
- Atomic numbers: 6 and 7 (different).
- Mass numbers: Both are 14 (same).
- Conclusion: They are not isotopes.

6. **Option 4: X (84, 34) and Y (85, 36)**:
- Atomic numbers: 34 and 36 (different).
- Mass numbers: 84 and 85 (different).
- Conclusion: They are not isotopes.

7. **Final Conclusion**:
- The pairs that are not isotopes are Option 3 (X 14, 6 and Y 14, 7) and Option 4 (X 84, 34 and Y 85, 36).

### Summary of the Answer:
The pairs which are not isotopes are:
- Option 3: X (14, 6) and Y (14, 7)
- Option 4: X (84, 34) and Y (85, 36)